FAT32 should be the most suitable for USB flash drive. However, the biggest problem of this format is that it cannot store a single file with a capacity greater than 4G. But I don't think anyone will copy HD movies or DVD images with a USB flash drive. If nothing else, his speed and waiting time will make you collapse. Otherwise, the format is mature and easy to use.
NTFS format has many advantages, such as large file support, security, retrieval performance, etc., but all these are in vain in the face of the snail speed of U disk. Moreover, ordinary U disk can't be formatted as NTFS. Only when the USB flash drive is made into a hard disk type USB flash drive, such as Netac's previous dual boot USB flash drive, can it be formatted as NTFS.
To sum up, NTFS is a good thing, but it is more suitable for mobile hard disk than USB flash drive. The best format of U disk is FAT32.